Comparing the role of annealing on the transport properties of polymorphous AgBiSe and monophase AgSbSe.

AgBiSe and AgSbSe, two typical examples of Te-free I-V-VI chalcogenides, are drawing much attention due to their promising thermoelectric performance. Both compounds were synthesized melting and consolidated by spark plasma sintering. The role of annealing on the transport properties of polymorphous AgBiSe and monophase AgSbSe was studied. Annealing has a greater impact on AgBiSe than AgSbSe, which is ascribed to the temperature dependent phase transition of AgBiSe. Unannealed AgBiSe shows p-n switching, but annealed AgBiSe exhibits n-type semiconducting behavior over the whole measurement temperature range. By performing high-temperature Hall measurements, we attribute this intriguing variation to the change in the amount of Ag vacancies and mid-temperature rhombohedral phase after annealing. Both AgBiSe and AgSbSe exhibit low thermal conductivity values, which are ∼0.40-0.50 W m K for AgSbSe and ∼0.45-0.70 W m K for AgBiSe, respectively. The maximum value of AgBiSe is enhanced from 0.18 to 0.21 after annealing. Pristine AgSbSe presents a value as high as 0.60 at 623 K, although slight deterioration emerges after annealing.